High-pressure gas process



March 21, 1939. w. H. VAUGHAN HIGH PRESSURE GAS PROCESS .INVENTORWILLIAM H VAUGHAN BY @Qa/g ATTORNEY Patented Mtr.Y 21, `1939HIGH-PBESSURE GAS PROCESS william n. Vaughan,

Tidewater Oil Company poration o! Palestine, Tex., Associated OilCompany, Okla., a corporation of Delaware,

of Delaware, Delaware aasignor to Tulsa, and Seaboard Dallas, Tex., acor- Application August 12, 1938, Serial No. 224,471

10 Claims. This invention relates high pressure gas. and for recoveringgasoline gas which normally vapor.

In my former application, Serial Number 160,192, filed August 20, 1937,now matured into particularly to a process constituents from naturalcontains water or water Patent NO- 2,133,774, issued October 18,1938,-

there was disclosed a process for the recovery of desirable constituentsfrom gas which wasinitially at a high pressure within the retrogradecondensation range of said constituents, vand specically from gas whichwas at an initial pressure above 700 pounds per square inch. Asvdisclosed in said former application, the recovery process consisted incooling the gas suiliciently to condense the desirable constituents,while reducing the pressure substantially only within the 20 retrogradecondensation range of said constituents at the condensation temperature.This process is particularly applicable to the recovery of desirableliqueiiable constituents from gas produced from high pressure gas wells,from which the raw gas is ordinarily available at the well head atpressures ranging from about '700 pounds to 3000 or more pounds persquare inch. In conducting the recovery process in accordance with theinvention disclosed in my earlier application, the initial pressure wasreduced only a minimum amount in order to conserve to a maximum degreethe initial pressure energy of the gas, whereby the gas could bereturned to subsurface reservoirs for repressuring purposes with It; aminimum amount ofv re-compression and to thus provide a process by meansof which an elicient recovery of desirable liqueable constituents waseffected and the residue gas made available for return` to thesub-surface reservoirs under highly economical conditions.

Thus by means of the aforementioned process, an eiiicient extraction ofdesirable liquefiable constituents could be effected while reducing theinitial pressure of. the gas only 200 or 300 pounds per square inch inmany cases. In cooling the gas sufficiently to condense the desiredconstituents under the high pressures at which the process is conducted,it has been found that, due to the quantities of water present normallyin natural gas, crystalline hydrates of the natural gas constituentswere produced and resulted in clogging of the recovery apparatus withdetrimental keilects upon the eiiiciency of the process.

It has now been found that such detrimental hydrate formation may beefficiently controlled to a process for the recovery of desirableliquefiable constituents from (Cl. (i2-175.5)

and prevented by be added vto the certain novel steps which mayaforo-described The resulting combination process forms the subjectmatter of Serial'Number 160,192, refe this invention and constitutes acontinuation-impart of my earlier application rred to above.

The improved process of this invention comprises, in combination withthe basic steps of my earlier invention, the additional steps ofregulating the quantity of water normally contained 1n natural gas as itleaves the well,

covery of desirable liqueable constituents to f prevent or inhibit theformation of hydrates in the process.

Regulation of the contained in the ygas as it le by regulatedmaintenance quantity of water normally aves a well is eiiected of theinitial pressure of the gas from the well head through the processingsteps to the nal pressure reduction step, and the dehydration of gasduring proces' sing is eiected by the injection directly into intimatemixture with drating agent which the gas of a suitable dehy` issubstantially immiscible with the gas constituents, all as will be morefully described hereinafter.

Therefore, it is a vention to recover desirabl uents fromr high pressureprincipal object oi.' this in e liqueiiable constitgas which normallycontains water or water vapor.

high

recover desirable liquefipressure natural gas pressure within theretroof said constituents r water vapor.

to recover desirable from high pressure natural gas while dehydratingthe gas to prevent or inhibit the formation of hydrates of theconstituents of the gas.

Other and more specic objects and advantages of my new invention willbecome apparent from the following detailed description and theaccompanying drawing which diagrammaidcally illustrates an arrangementof apparatus suitable for practicing the Referring to the drawing, natesan oil or gas well is mounted a pressure contr vnew invention.

the numeral I desigadapted to Supply high pressure gas to the process.

A Pipe 2, in which ol valve 3, leads from the top of well I to a fieldseparator or scrubber 4 having a valved drain pipe 5 connected to thebottom thereof and a gas discharge pipe 6 leading from the top thereofsuccessively through the tubes of a pair of more 0r l ess conventionaltype heat exchangers 1 and 8. From the tubes of heat exchanger 8 a pipe3 leads into the upper portion of a separating chamber III. A pressurereducing valve II is mounted in pipe 9, preferably at a point closelyadjacent to separating chamber I0. From the top of separating chamberI0, a pipe I2, having a valve I3 therein, leads to the shell of heatexchanger 1, which is provided with an exit'pipe Il. A pipe I5, having avalve: I6 therein, controlled by a conventional liquid level controllerI1, leads from separating chamber I at a point intermediate the top andbottom thereof. A pipe I8, having a valve I9 therein controlled byanother liquid level controller 20, leads from the bottom of separatingchamber I0 and connects into pipe 6 at a point in advance of heatexchanger 1. A pump 2| is interposed in pipe I8 between separatingchamber I0 and pipeI 8 and a valve 22 is mounted in pipe I8 between thepump and the separating chamber. A valved drain pipe 23 is connected topipe I8 at a point between valves I9 and 22. A pipe,24, having a valve25 therein, leads from a tank 28 and connects into pipe I8 between pump2l and valve 22. A pipe 21 connects into the shell of heat exchanger 8,which is provided with an exit pipe The above described apparatus isemployed in the following manner in conducting the process of thisinvention:

Gas, containing desirable liqueable constituents, such as propane,butanes, pentanes, and heavier hydrocarbons ordinarily present innatural gas, and under a high pressure within the retrogradecondensation range of these constituents, is drawn from well i throughpipe 2 and under control of valve 3 into scrubber l. The pressure of thegas under these conditions is above '100 pounds per square inch and maybe as high as 3000 pounds per square inch or more. The gas when itleaves the bottom of the well will ordinarily contain water, which, atthe pressure and temperature existing in the well, will be in the vaporphase in the gas. As the gas 'ilows from the bottom of the well to thetop, the temperature of the gas, which may be 200 F. or higher at thebottom of the well, will be reduced by heat exchange with the 'coolerstrata as it approaches the top ofthe well, and some. of the water willbe condensed and remain in the Well. However, at the top of the well, acertain amount of water vapor will remain in solution in the gas in anamount which is determined by the pressure and the temperature of thegas at the top of the well. This water vapor will remain in the gasuntil removed Vin subsequent steps of the process, as will later bedescribed.

As the gas ilows through scrubber 4, any mechanically entrained waterand gas condensate will separate from the gas and will collect in thebottom of the scrubber to be withdrawn therefrom through pipe 5. Thegas, freed of entrained material, then ows through pipe 6, thence inseries through the tubes of heat exchangers 1 and 8, wherein the gas isfurther cooled, in a manner to be more fully described hereinafter, andfrom heat exchanger 8, the gas ilows through pipe 3 into separatingchamber I0. Before entering separating chamber I0, the pressure on thegas is reduced by means of pressure reducing valve II. The amount ofpressure reduction thus effected will be an. amount which issubstantially only within the retrograde condensation range of thedesirable liqueiable con-1 stituents at the temperature to which the gaswill be nally cooled, both by the cooling effected in heat exchangers 1and 8 and by the final cooling resulting from the expansion of the gasin separating chamber I0 as a result of the reduction in pressure. Itwill be noted that the initial pressure of the gas, except for suchreduction as occurs from pressure drop in passage through the apparatus,ismaintained throughout 'the cooling steps conducted in heat exchangers1 and 8 and that this pressure is reduced only after the gas has beencooled in these heat exchangers.

Under these pressure conditions and at the temperature to which the gasis cooled in effecting the recovery of the desired constituents, thewater vapor present in the gas tends to form crystalline hydrates of atleast some of the constituents of the gas, and these hydrates tend toclog the apparatus and greatly reduce the efllciency of the heatexchange in exchangers 1 and 8. To dehydrate the gas and to thus inhibithydrate formation, a quantity of a suitable dehydrating agent,preferably o f relatively high specific gravity and substantiallyimmiscible with the gas constituents, such for example as concentratedaqueous solution of calcium chloride, is drawn by means of pump 2| fromtank 26, in which a supply thereof is maintained, throughpipe 24 andvalve 25 and is discharged through pipe I8 into pipe i in which theagent is intimately mixed with the high pressure gas and absorbs thewater vapor therefrom, thus dehydrating the gas' and inhibiting hydrateformation.

The dehydrating agent accompanies the gas stream in its flow throughheat exchangers 1 and 8 and pipe 9 into separating chamber I0. Upondischarge of the cooled mixture through pressure reducing valve II intoseparating chamber III, the iinal cooling incident to the expansion ofthe gas will cool the gas to the nal desired temperature at which thedesired constituents of the gas will condense and will separate fromuncondensed gas and fall to the bottom of separating chamber III. Thedehydrating agent will also tall to the bottom of the chamber and sinceit is of greater specic gravity than the gas condensate andsubstantially immiscible therewith, it will collect in the bottom ofseparating chamber III in a pool which will underlie the condensed gasconstituents. The resulting levels in chamber III of the dehydratingagent and of the gas condensate are respectively designated in thedrawing by the broken lines 23 and 38.

The condensed gas constituents are continuously withdrawn fromseparating chamber I0 through pipe I and valve I6 at a rate controlledby liquid level controller I1. The dehydrating agent is likewisecontinuously withdrawn from the bottom of separating chamber I Ilthrough pipe I8 and valve I3 by means of pump 2I which discharges thewithdrawn dehydrating agent to pipe 8 for recycling in the system. Therate at which the dehydrating agent is withdrawn from chamber I0 iscontrolled by means of liquid level controller 20 to maintain a constantlevel of the agent in the chamber. As the dehydrating agent circulatesthrough the process it becomes diluted bythe water which it absorbs fromthe gas, and from time to time a portion of the dilute agent may bewithdrawn from the system through pipe 23 and sent to a suitablereconcentrator if desired, or entirely removed from the process. Tomaintain a constant supply of dehydrating agent of suitable quality,fresh material is added to the system from tank 28 as previouslydescribed.

As noted above, the expansion of the gas through valve II intoseparating chamber l0 cools the gas to the final desired temperature andcondenses the desired constituents, which, together with the dehydratingagent, separate from uncondensed gas in the separating chamber. Theuncondensed gas, which is now at a low temperature, is discharged fromthe top of the separating chamber and flows through pipe I2 to the shellof heat exchanger 1 where it serves to partially cool the mixture of rawgas and dehydrating agent introduced into the tubes of the exchangerfrom pipe 6. The uncondensed gas, after passing through heat exchanger1, is discharged therefrom through pipe II to be further employed in anydesired manner. The uncondensed gas may be sent to a compressor (notshown), which recompresses the gas to a pressure somewhat above itsoriginal pressure and returns it to the subsurface stratum from which itwas drawn originally for repressuring this stratum, or to anotherformation, such as an oil producing formation, to aid in the productionof oil, or it may be used for any other purpose for which high pressuregas may be useful.

Intermediate cooling of the raw gas is effected in heat exchanger 8 bymeans of any suitable refrigerating medium which is introduced into theshell of exchanger 8 through pipe 21 and discharged therefrom throughpipe 28 after further cooling the stream of raw gas and dehydratingagent flowing through the tubes of the exchanger en route to separatingchamber I0 as previously described. Various refrigerating mediums may beutilized in heat exchanger 8, such as expanded liquid propane, orammonia, or refrigerated brines.

Since the dehydrating agent has been cooled to a very low temperature inits passage through heat exchangers l and 8 and by the expansion of thegas in separating chamber I0, it serves, upon recirculation directlyfrom the separating chamber to pipe 8, as an additional cooling mediumfor cooling the raw gas to the desired temperature and thus reduces thecost of refrigeration for the cooling steps conducted in heat exchanger8.

In one specific plant operated in the manner heretofore described, thetemperature of the gas leaving the well was about 110 F. Suiiicient colddehydrating agent from separating chamber l0 was circulated in thesystem to lower the temperature of the gas entering heat exchanger 'l toabout 95 F. Heat exchange with the expanded gas in exchanger l furtherreduced the temperature of the gas to about 46 F. and intermediatecooling with expanded ammonia in heat exchanger 8 additionally reducedthe temperature ofthe gas to 24 F. from which the gas was cooled to afinal temperature of 9 F. by expansion through valve Il from an intialpressure of 1350 pounds per square inch to a final pressure of 1150pounds per square inch. About 90 percent of the propane and heavierconstituents contained in the raw gas was condensed and withdrawn asproduct from separating chamber I0. No hydrate formation occurred in theapparatus. n

As noted above, and as disclosed in my earlier application. SerialNumber 160,192, the recovery of desirable liqueiiable constituents fromthe raw gas is effected by cooling the gas, while reducing the pressuresubstantially only within the retrograde condensation range of theconstituents. Thus in processing a gas which is initially at a highpressure within the retrograde condensation of the desired constituents,i` e., above 700 pounds per square inch, it is suiliclent to reduce thepressure only within this limited range to effect substantiallycompletecondensation of the desired constituents by cooling of the gasto a suitable temperature. 'I'his temperature generally ranges fromabout -5 F. to 40 F., but may be higher or lower depending largely uponthe nature of the constituents to be recovered and upon the pressure itis found most economical to employ. By reducing the pressure within thespecified limited range, only a minimum amount of the initial pressureof the gas is dissipated. and the resulting relatively high pressure ofthe residue gas permits economical recompression thereof for return tosub-surface strata. Pressure reduction within the retrogradecondensation range is absolutely essential for the condensation ofmaximum quantities of desirable constituents, otherwise theseconstituents would remain in the vapor phase under the high pressureconditions set forth, regardless of the extent of cooling applied to thegas. 'I'his effect was described in detail in the referred-to earlierapplication.

The injection into the high pressure gas of a relatively high specificgravity dehydration liquid which is substantially lmmscible with the gasand the condensed constituents thereof, while injected primarily for thepurpose of dehydrating the gas and inhibiting hydrate formation, alsoserves the additional purpose of providing another valuable coolingmedium for the gas as previously described, and appears to have stillanother valuable function, which is due to its relatively high specificgravity. When the mixture of gas and dehydrating agent is introducedinto separating chamber` I0, the expansion of the gas under the extremepressure conditions described, tends to finely atomize the gasconstituents which are condensed by the final cooling incident to theexpansion of the gas, and a substantial proportion of `the condensate,in this finely atomized state, tends to remain entrained in theuncondensed gas. However, the relatively high specific gravitydehydrating agent, present at the point of expansion, appears to act asa mechanical scrubber and appears to coalesce the fine condensateparticles and wash them from the uncondensed gas and thus prevent theirloss. Upon precipitation of the dehydrating agent and gas condensate inthe lower portion of the separating chamber, the relatively largedifference in the specific gravities of the gas condensate and thedehydrating agent results in a quick settling and clean separation ofthe dehydrating agent from the gas condensate. The dehydrating agentfound to be most satisfactory for use in this process is a concentratedsolution in water of calcium chloride, preferably a solution of about 35B. Other salts of similar nature may be used successfully.

'Ihe step of maintaining the initial pressure from the well head throughthe earlier cooling steps to the point of final pressure reduction, isparticularly advantageous in reducing the quantity of water vapor in thegas, which must be removed bythe dehydrating agent. While the condensaterecovery process could be conducted fairly successfully by firstreducing the initial pressure to the final desired pressure at the wellhead, by manipulation of valve 3, such reduction in pressure wouldimmediately result in the re-evaporation into the gas of at least a partof the water which was condensed from the gas in passage to the top ofthe well, and would thus increase the 'water content of the gas passingthrough the recovery steps of the process and'would thereby increase thedifficulty and the cost of Adehydration of thel gas. f

Thus vin, the above specic example, gas at n 1350 pounds per square inchand 110 F. will contain about 6.5 gallons of water per million cubicfeet, while at 1150 pounds per square inch and 110 F., the gas willcontain about 7.5 galvheat exchange of the cooled expanded gas'with theraw gas prior to expansion thereof. However, under most conditions thismethod of coolingis preferably supplemented by additional cool- 20 ingeffected by an extraneous cooling medium.

such as by expansion of ammonia through heat exchanger 8, as abovedescribed.

From the foregoing it will be seen that the improved process of thisinvention comprises a process for the recovery of desirable'liquefiableconstituents from gas which is initially at a pressure within theretrograde condensation range of said constituents, and which consistsin initially cooling the gas to a temperature below its initialtemperature, maintaining said initial pressure on the gas during saidcooling, thereafter reducing the pressure on the gas substantially onlywithin the retrograde condensation range of saidconstituents to therebycondense said constituents and dehydrating the gas during said coolingby intimately mixing therewith-a relatively high specic gravity liquiddehydrating agent, which is substantially immiscible with the l from thedehydrating agent.

What I claim and desire to secure by Letters Patent is:

l. The process of recoveringdesirable liquefiable constituents fromnatural gas containing water and which is initially at a high pressurewithin the retrograde condensation range of said constituents whichcomprises, intimately mixing with said gas a dehydrating agent Vwhich'issubstantially immiscible with said constituents, cooling the resultingmixture of gas and said agent sufficiently to condense saidconstituents, maintaining said high pressure on said gas during saidcooling, thereafter reducing said high pressure substantially onlywithin the retrograde condensation range 'of said constituents at thereduced temperature, and separating the resulting condensed constituentsfrom uncondensed gas and dehydrating agent.

2. 'I'he process of .recovering desirable liquenable vconstituents from`natural gas containing water and which is linitially at a high pressurewithin the retrograde condensation range of said constituents whichcomprises, intimately mixing l with said gas a dehydrating agent whichis substantially immiscible with said constituents, precooling theresulting mixture of gas and said agentwhile under said high pressure toa `temperature below the initial temperature of the gas but above thei'lnal desired temperature for condensation of said constituents, thenreducing said high pressure substantially only within the retrogradecondensation range ofsaid constituents at said iinal temperature tothereby further cool saidr gas to said iinal temperature, and separatingthe resulting condensed constituents from uncondensed gas and saiddehydrating agent.

3. The process of recovering desirable liqueiiable constituents'fromnatural gas containing water and which is initially at a high pressurewithin the retrograde condensation range of said constituents whichcomprises, intimately mixing with saidgas a. liquid dehydrating agentwhich is substantially immiscible with said contion effect produced inthe gas by the reduction n in pressure to accomplish the aforesaidcooling, and returningA the dehydrating agent into said `intimate mixingwith fresh natural gas entering the process.

4. 'I'he process of recovering desirable liqueiable constituents fromnatural gas containing water and which is initially at a high pressureabove '700 pound per square inch which comprises, intimately mixingwith. said gas a dehydratirm agent which is substantially immisciblewith said constituents, cooling the resulting mixture to a suitablecondensation temperature for said constituents, maintaining said initialpressure on said mixture during said cooling, thereafter reducing theinitial pressure within a range above 700 pounds per square inch, andseparating the resulting condensed constituents froml uncondensed gasand dehydrating agent.

5. 'Ihe process of recovering desirable liquenable constituents fromnatural gas containing water and which is initially at a high pressureabove 700 pounds per square inch which comprises, intimately mixing withsaid gas a dehydrating agent which is substantially immiscible with saidconstituents, cooling the resulting mixture to a suitable condensationtemperature for said constituents, maintaining said initial pressure onsaid mixture during said cooling, thereafter reducing the pressuresubstantially only within the retrograde condensation range of saidconstituents at said condensation temperature but not below 700 poundsper square inch, and separating the resulting condensed constituentsfrom uncondensed gas and dehydrating agent.

6. The process of recovering desirable liquefiable constituents fromnatural gas containing 55 water and whichisrinitially at a high pressureabove '700 pounds per square inch which comprises, intimately mixingwith said gasa dehydrating agent, ilowing the resulting mixture in aconiined stream through a series of cooling zones'to cool the gas whilethe gas is maintained 'under substantially said initial pressure, nallyexpanding said gas to a lower pressure above 700 pounds per square inchin an enlarged separating zone to thereby finally cool said. gas tothedesired condensing temperature, therein separating uncondensed gas fromcondensed constituents and dehydrating agent, withdrawing saiduncondensed gas from said separating -zone and passing same through oneof said cooling zones in indirect heat exchange relationship with saidstream of gas. I

7. The process of recoveringvdesirable liqueiiable constituents fromnatural gas containing water and which is initially at a high pressureabove 700 pounds per square inch which comprises, intimately mixing withsaid gas a dehydrating agent, iiowing the resulting mixture in aconl'ined stream through a series of cooling 5 zones to cool the gaswhile the gas is maintained under 'substantially said initial pressure,ilnally expanding said gas to a lower pressure above 700 pounds persquare inch in an enlarged separating zone to thereby ilnally cool thegas to the desired condensing temperature, therein separatinguncondensed gas from condensed constituents and dehydrating agent,separately withdrawing from said separating zone condensed constituents,uncondensed gas and said dehydrating agent, and continuously circulatingdehydrating agent from said separating :one to said stream of gas owingthrough said cooling zones.

a. 'rile process of recovering desirable uquen- 30 able constituents'from gas containing water and which is initially at a high pressurewithin the retrograde condensation range of said constituents whichcomprises, intimately mixing with said gas an aqueous solution ofcalcium chloride, u cooling the resulting mixture suiilciently tocondense said d'esirable constituents, maintaining substantially'saidinitial pressure on said gas during said cooling, thereafter reducingsaid pressure substantially only within the retrograde con- .o densationrange of said constituents'at the reduced. temperature, and separatingthe resulting condensed constituents from uncondensed gas and saidcalcium chloride solution.

9. The process of recovering desirable liqueilable constituents fromnatural gas containing water and which is initially at a high pressureabove 700 pounds per square inch which comprises, intimately mixing withsaid gas an aque- 5 ous solution of calcium chloride, cooling theresulting mixture to a suitable condensation temperature for saidconstituents, maintaining said initial pressure on said mixture duringsaid cooling, thereafter, reducing the initial pressure with- 10 in arange above 700 pounds per square inch. and separating the resultingcondensed constituents from uncondensed gas and said calcium chloridesolution.

10. The process of recovering desirable llqueil- 15 able constituentsfrom natural gas containing water and which is initially at a highpressure above 700 pounds per square inch which comprises, intimatelymixing with said gas an aqueous solution ofcalcium chloride, cooling theresulting mixture to a suitable condensation temperature for saidconstituents, maintaining said initial pressure on said mixture duringsaid cooling, thereafter reducing the initial pressure within a rangeabove "100 pounds per square inch, sepa- 25 ra ing the resultingcondensed constituents from uncondensed gas and said calcium chloridesolution, and returning said calcium chloride solution to the aforesaidintimate mixing with said gas.

WILLIAM H. VAUGHAN.

